IEEE (Institute of Electrical and Electronics Engineers) 802.16 standard provides a technology and protocol for supporting broadband wireless access. Standardization of IEEE 802.16 began in 1999 and was approved in 2001 as IEEE 802.16-2001. IEEE 802.16 is based on a single carrier physical layer called ‘WirelessMAN-SC’. In the IEEE 802.16a standard approved in 2003, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ were further added to the physical layer. After standardization for IEEE 802.16a was completed, revised IEEE 802.16-2004 standard was approved in 2004. To correct bugs and errors for the IEEE 802.16-2004 standard, IEEE 802.16-2004/Cor1 was completed in 2005 under the format of ‘corrigendum’.
An error compensation scheme for ensuring reliable communication includes a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. The FEC scheme corrects errors of a receiving stage by adding a redundant error correction code to information bits. The ARQ scheme corrects errors through data retransmission and includes stop-and-wait (SAW), go-back-N (GBN), and selective repeat (SR) ARQ. Although the FEC scheme is advantageous in that a time delay is small and no additional information transmitted and received between transmitting and receiving stages is necessary, system efficiency in good channel environments is lowered. The ARQ scheme improves transmission reliability, but a time delay occurs and system efficiency in bad channel environments is lowered. To overcome those shortcomings, a HARQ scheme which combines FEC and ARQ has been proposed. The HARQ scheme confirms whether data received by a physical layer includes errors which can not be decoded and requests retransmission upon occurrence of errors, thereby improving performance.
A HARQ mode includes chase combining and incremental redundancy. Chase combining combines error-detected data with retransmitted data without discarding the error-detected data. Incremental redundancy incrementally transmits redundant information added to retransmitted data, thereby reducing the burden of retransmission.
If no error is detected in received data, a receiver transmits an acknowledgement (ACK) signal as a response signal to inform a transmitter that data has been successively received. If an error is detected in received data, the receiver transmits a negative acknowledgement (NACK) signal as a response signal to inform the transmitter that an error has been detected. Upon receiving the NACK signal, the transmitter can retransmit data.
In a HARQ scheme, a receiver basically attempts to correct errors of received data and determines whether to retransmit data using an error detection code. A cyclic redundancy check (CRC) may be used as the error detection code. If an error in received data is detected through a CRC detection process, the receiver transmits a NACK signal to a transmitter. Upon receipt of the NACK signal, the transmitter transmits proper retransmission data according to a HARQ mode (chase combining or incremental redundancy). When receiving the retransmission data, the receiver combines previous data with the retransmission data to perform decoding, thereby improving reception performance.
At a high data transmission rate of a maximum of a few hundred of Mega bits per second (Mbps), the length of an information block transmitted within a unit transmission interval is abruptly increased. If one CRC is attached to a large-size information block, even a small number of bit errors generated in the information block, size of which is increased, causes an error in all bits. Accordingly, a receiver transmits a NACK signal for the entire information block and a transmitter retransmits the entire information block. This may directly result in a decrease in overall system throughput.
Meanwhile, in future generation mobile communication systems, for example, a 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution)-Advanced system and an IEEE 802.16m system, a multi-carrier support mode is being discussed. In the multi-carrier support mode, a plurality of bandwidths, that is, a successive or intermittent combination of bandwidths in an existing system (e.g., a 3GPP LTE system or an IEEE 802.16e system) is controlled by one common medium access control (MAC) so that a common MAC protocol data unit (PDU) can be transmitted through multiple carriers. If only one CRC is attached when transmitting a large-size information block, i.e., a common MAC PDU, through multiple bands specified by multiple carriers, retransmission of all information bits may be demanded due to a small number of bit errors, or a HARQ process delay may occur.
Hence, in a mobile communication system demanding high transmission rate and/or supporting the above-described multi-carrier mode, a method for efficiently performing a HARQ scheme is needed.